1. Field of the Invention
The invention relates to antennas such as those used in office equipment and portable electronic devices, and particularly to dual-band antennas for radiating electromagnetic signals of different frequencies.
2. Related Art
Due to increasing market demand for mobile communication products, the development of wireless communication products and systems has rapidly advanced. Many wireless communication standards have been drawn up and implemented. Perhaps the most appealing standard is 802.11, drawn up by the Institute of Electrical and Electronics Engineers (IEEE) in 1997. The IEEE 802.11 standard provides many new functions regarding wireless communication, and provides many new methods for communication between wireless communication products of different companies.
In August 2000, the IEEE amended 802.11 such that 802.11 became a joint standard of the Institute of Electrical and Electronics Engineers (IEEE), the American National Standards Institute (ANSI) and the International Standard Organization (ISO). Furthermore, two more important protocols were added: IEEE 802.11a and IEEE 802.11b. IEEE 802.11a and 802.11g products are expected to work at the dual frequencies of 5 GHz and 2.4 GHz, respectively. Therefore, if a wireless communication product uses the two protocols simultaneously, more than one antenna is required. The addition of one or more antennas, however, not only increases the base cost and installation cost of the communication product, but also means that the communication product occupies more space. This makes it very difficult to reduce the overall size of the wireless communication product to a more convenient size.